Signal system



Marh 26, 1940. N, F, SHOFSTALL 2,195,290

SIGNAL SYSTEM Filed Aug. 20, 1938 Nortony FT Shofstall b )Wfl/'7 l? y His/Attorney.

Patented Mar. `26, 19x40r SIGNAL wie "PAT-ENT? orFicE@ SYSTEM lNorton 1F, Shofstall, Stratford, Conn., assigner to `General Electric Company, a corporation of l New York s i Application August 20,

Myinvention relates-to signal systems'andmore particularly toy oscillation generators utilized in such systems.v It has furgone 'of Aits `objects to provide novel and improved *means for con- 5 trolling the amplitude of voscillations generated by such oscillation generators;

My invention relates-'more particularlyto such oscillation generators utilized in superheterodyne radio receivers in Which the frequency of oscillations produced thereby yis regulated by the inter` mediate frequency produced by combining such oscillations With received signal currents. Such systems are commonly utilized to maintain theintermediate frequency constant irrespective of variations in the frequency of the received signal, or in the frequency of oscillations' produced by the local oscillator.v In such systems `the frequency of the local oscillator l is commonly regulated by means ofY an electron 'discharge 'device having 20 its electrodes connected to simulate ka reactance, across" the frequency 'determining circuit of the local oscillator and having va grid the bias ionv which is controlled 'by variations inifrequency of Y the intermediate frequency currents. 1n 'this way, desired control of thefvalue vof simulated reactance andk hence desired regulation of the frequency of oscillations'produced isobtaine'd.

, One of the objects of my invention is to imy prove the operation'of suchA systems with'y respect '30 to the amplitude'ofoscillations produced.

A further object oi my invention issto provide means automatically to counteract the eiectof such systemsupon the amplitude of oscillations produced. u y

e The novel featuresjwhich I believe ,tor be char-l acteristic of myl invention are s'et forth with particularity in theappended claims.. My irivention itself, however, -both as to its organiza-.- tion and method `of loperation, ltogether with "40 yfurther objects and advantages thereohmay best i vbe understood by reference to the follotvling"de'-.

scription takenv in connection with the accompanying drawing in which the single gure rep resentsr an embodimentof my invention. y s

Referring tothe drawing, I have shown therein` a radio' receiver embodying myinvention;4 this receiver comprising an antenna I `Wliich connected through azitransiormer 2 to one grid 3 of an electron discharge device', 4'. YThis discharge device is connected to 'operate asa first detector',v

or superheterodyne converter, oftheiadio -re-fy ceiver. A second grid 5 of' this discharge device is connected'to lthe control grid 5` ofy the electron discharge device 'L which `is 'connected tooperate as an' oscillation 'g'eneratorto produce local oscila `193g, Serial No. 225,935

Ylations lto combine with ther received oscillations in lthe superheterodyne convertenthereby to produce oscillations of the so-called Aintermediate `frequency. .These latter oscillation-s appear I-in the output circuitof thedischarge device 4 and are, if desired, amplified in an intermediate frequency amplifier 3l and supplied through transformer f3 to -a second detector comprising diodes vIt and/Il. The anodes of the -tWo discharge devices It and'gI-I are connected to oppoo site terminals ofthe secondaryl Winding of -trans- 'former 9 and the vcathodes thereof are connected 'together through"resistances I2' and-,I3 vfor a vpurpose later to be described. The'cathode of "discharge vdevice It .is connected through re- 15 sistance I4 to la point on bleeder resistance I5 which is negative With respect fto ground. v'This bleeder resistance `connected across a source yof unidirectional operating Voltage It and lis grounded atg an intermediate point :thereof as 20 indicated at il'. This cathode-is also lgrounded for alternating v'current-s by condenserv I8. The

cathode of discharge device II is yalso grounded through condenser l5", which is a conventional Yby-#pass condenser. Tocomplete the `,circuit for 25 rectifier' currents Aproduced .bydischarge devices- Isand II the vpoint between rsistances i2 and 13;- which commonly are of Vsubstantially equal. vvalue,is connected lthrough conductor`l9 to the midpoint oi the secondaryW-inding of `transform- '30 er 9, a suitable resistance capacity ylter comprising resistance 2t., and condensers 2I being incorporated in this connection. l f

The audio output from the 'receiver may betaken between ground and conductor 22,Which is connectedat the point between'resistances I2 and I3 and uponfwhich signlal oscillations appear.

v AThe local oscillator, comprisingy electron dischargedevice'l, may be of any'suitableconventional type, and isv shown as comprising an elec- '40 -tro`ndischarge device having a controlgrid '6,*a screen grid 23, and a suppressor grid 24 arranged in the conventional manner and'spaced at Vdifferent distancesl from the cathode and anode, as indicated. The frequency determining circuit 25 '45 yof .the oscillator isU'con'nected rbetween the conv trol grid andthe cathode, and the'inductance rthereof iscoupled to 'an inductance 2S which is rconnected between' the anode yand cathode of the discharge device therebyto produce ythe neces- 50 v are supplied through conductor '5I from.' the` 55 l 70 maryand secondary windings 48 and 49 of trans-V in the anode circuit of the' discharge device 4v.

grid of discharge device 1 to a control grid 5 of theconverter 4.

To control the frequency of oscillations 'produced by the discharge device 1, a further electron discharge device 28 is employed, this device having its anode and cathodeconnected between groundy and a point on the inductance of the frequency determining circuit 25. The grid 52 of this discharge device is connected through resistance' 29 and conductors 38 and 21 to the cathode of diode II whereby it is subjected to a bias or control potential with respect to ground dependent on the potentials on resistances I2 and i3. The grid ofv this discharge device is also connected through condenser 3I to an intermediate point on a path between the anode and cathode of discharge device 28, this path comprising resistance 32 and condenser 33. v

The cathode of the discharge device 28 is :biased positively with respect to ground by means of the usual cathode bias resistor 34 which is by-passed with respect,v to currents of radio frequency byV condenser 35.

Operating potentials for the various discharge devices employed are supplied from the bleeder resistance I5 which may be connected across the output of any suitable rectier. It will be seen that the screen grid potential for the converter 4,

and oscillator 1, as well as similar potentials forr vice 28, is connected to thecontrol conductor 21" thro-ugh resistance 38 and connected to ground through condenser 39. The latter elements cornprise the usual resistance capacitance 'lterto prevent the supply of alternating currents from conductorZl tothe suppressor grid..

The operation of my devicewill now be ex# plained in greater ldetail. y

Signal Voscillations received upon the antenna I are Aimpressed by transformer Zuupon a tuned cir,` f

cuit comprising the secondary winding of this transformer'and tuning condenser 48, which condenser is arranged for uni-control with a condenser 4I of the frequency determining circuit 25,

of the oscillator. When the circuit comprising condenser4 is tuned thereby to the frequency of oscillations to be received, the frequency determiningcircuit 25 is tuned to a corresponding frequency, usually greater than the frequency of the received signal by an amount equal to the intermediate frequency, which the amplifiers 8 are adapted to amplify. Usually this intermediate v frequency is of about 455 kilocycles. Accordingly, the received signal oscillations which appear across condenser 46 and those produced by the local oscillator are supplied respectively to the two control grids 3 andz' of the converter 4; thereby to produce currents of the intermediate frequency These currents are amplified by intermediate fre-A quency amplifier 8 and are supplied through the transformer 9 tothevdiodes I8 and II. The pri-A forrner 9. are tunedto this intermediate frequency by condensers 50 and 5I connected respectively thereacross. The upper terminal of the primary winding 48 also connected through a. condenser `phase with respect to the potential 43 to the midpoint on the secondary Winding 49 of this transformer.

This transformer operates to-supply to the diodes I0 and I I equal electromotive force when the intermediate frequency is of the exact value to which the circuits of thetransformer are tuned for operation. If this` frequency varies in one direction then the transformer supplies a greater potential to one of the diodes I0 or I I than it does to the other. If the frequency varies in the opposite direction then the greaterpotential is sup- -plied to the opposite diode. These effects, as is now well understood, are produced by reason of the tuning of the primary and secondary windings at thisintermediate frequency and by reason of the action of condenser 43. The result is that the unidirectional potential which appears on resistance I3 is equal to that on resistance I2 when the intermediate frequency is of the exact value, and since these potentials are oppositely polarized thecontrol conductor 21 is negative with respect to ground byan amount determined by section 42 of the bleeder resistance I5.` Wheny the intermediate frequency varies in one. direction or the other, the control conductor becomes either more or lessnegative, dependent upon the direction of the variation of the intermediate frequency from the normal value. .This potentialof conductor 21 is supplied through resistance 38 to the suppressor grid 24 of local oscillator 1 and -alsothrough resistance 29'to the control grid 52 of the electron discharge device 28. l

' The anode and cathode'of discharge device 28, as previously stated, are connected across a .portion of the frequency determining circuit 25 of the oscillator. This discharge device is connected 'to simulatea reactance across ra portion of this frequencyv determining circuit, the, magnitude of the reactance `being varied by the potential 'on the control grid,` therebyto control the frequency determined by the'jcircuit 25. fTo effect this simulation of reactance by thev discharge device 28, its anode is .connected to ground through resistance 32 and condenser 33, andthe point therebetween iis connected' through condenser 3l to the grid, as previously described. Since the circuit comprisingresistance`32" and condenser 33` is capacitive, the potential'across` condenser 33 isfof .leading on the anode of discharge device 28, and since this potential is supplied through 'condenser'3l to the grid of dischargedevice 28 the potential on that grid, therefore, is .inf leadingphase Withrespect to the potential on" the anode. The current between the anode and cathode is displaced in phase'by. 180 degrees'froni'the gridpotential ofthe discharge device and, therefore, lags the anode voltage. vIn other words, the discharge device acts in the nature of an inductance, and controls the effective reactance of the portion of theoscillatng 'circuit 2 5' `across which it isL connected. Of course,"for the same" reason, were condenser 33 replaced by a'ninductancathe discharge device 28'would act inthe nature of a capacitance. 'The magnitude i of4 the current flowing through'the discharge device 28, and hence the magnitude of this simulated reactance, maybe varied by thepotential of conductor 21. When this potential is less'negative, the' simulated reactance of `discharge device 28 is reduced,l and when it ,is more negative, lthe vsimulatedgreactance is increased with the result that lthe frequency of oscillations produced by the os` cillator 1 is ldependent uponthe potential on conductor 2 14 and hence Aupon the frequency of the intermedie?? fregenal currents chansen afgegaan y j frequency of the -local oscillator-produced by varicathodes -are connected through conductor 41 lation ofthe potential onconductor 21,'may be *adj-usted to compensate for such variations in the Afrequency of ^the local oscillator as are produced through changes in the characteristics ofthe discharge device 'l produced during theheating up period, for example, and for other-causes. It may also compensate for changes in frequency of the "received signal, or for anyy effect tending todisturb the'intermediate frequency fromits normal value. Thus, for example, ifthe 'oscillator' frequencyitends to increase the intermediate 'frevquency increases and a potential is produced on conductor 2l, which varies the impedance of the discharge device v28 toan extent sufficient to produce a compensating change in the frequency produced by the local oscillator. If the oscillator frequency tends to decrease, the opposite compensa-ting action occurs. These Yeffects serve to maintain a constant intermediate frequency over a certain range of 'movement of the tuning control lfor lcondensers 4G and 4l thereby to obviate the necessity for accurate adjustment of these ycondensers to the frequency to be received.

In the operation of this system, however, when the conductor 21 becomes less negative andthe resistance of discharge device 28 is reduced and increased current from the oscillator flows throughr the discharge device 28, a considerable loading of the frequency determining circuit 25 is caused, this in turn having the effect of reducing the amplitude of oscillations produced by the oscillator I. In some cases the effect of this amplitude variation is very detrimental to the operation of the receiver due to the reduced translation efciency caused therebyv in the converter 4. In cases where the operating voltage is subject to variation this effect may cause the oscillator to cease oscillating altogether.

This effect may be overcome, however, and the amplitude of the oscillations produced by thev oscillator 1 may be rendered substantially constant, notwithstanding operation of the automatic frequency control circuit, by supplying the potential of the control conductor 21also to the suppressor grid 24 of the oscillator through resistance 3B. Thuswhen the conductorZT becomes 1 less negative, the suppressor grid 24 likewise becomes less negative with respect tothe cathode and, therefore, increases or tends to increase vthe amplitude of oscillations produced by the oscillator. This effect may be made just sufficient to compensatek for the opposite effect produced by the discharge device 28, thereby to maintain lthe amplitude of oscillations substantially congrid 24 and objectionable results.k produced thereby.

The potential with rrespect to ground on section 42 of resistance I5 is also supplied through resistances I4, I2 and 45 and automatic volume control conductor 46.to the grid 3 of discharge device 4 and other discharge devices within the equipment represented by rectangle 8. This potential may in some cases be too great for bias purposes on these devices. In order to adjust the bias voltage on these devices properly, their yiationsA in said intermediate frequency to conto adesired point on the 'bleeder resistance.. A

'1 "While Ihave showna particular embodiment of f A,my invention, it -will of course be understood that Ido not wish to be limitedthereto, since `different lInodifications both in the circuit 'arrangement and iny thev structure employed maya-i0 be 'made withoutdeparting fromthelspirit and scope `ofrny invention. I contemplateby the apzpended claims, therefore, to cover any such modifications as fall within the true spirit and scope of my invention. t' WhatI claim as new and desire to secure by Letters Patent of the'United States, is:

1.* Incombination, an electron discharge oscillator-,having an anode, a cathode, and a plurality of grids interposed between said anode and cath- '20 ode, alcircuit b'etweenfone of said grids and said cathode, a circuit between said anodeand catliode, a couplingbetween said circuits whereby oscillations are generated by said oscillatorjw means to produce ay unidirectional electromotive25 rforce having a magnitude dependent upon the frequency of said oscillations, means'to -oontrol ltliewfrequency of said oscillations -in response to l said electromotive force, said -lastme`ans operating to affect rundesirably the intensity of said oscillations, and means to supply said unidirectional electromotive force to another grid of said oscillator to compensate for said undesirable intensity variations of said oscillations.

2. In combination, an electron discharge oscillator, having an anode, a cathode, and a plurality of grids interposedb-etween said anode and cathode, a circuit between one of said grids and said cathode, a circuit between said anode and cathode, a coupling between said circuits whereby oscillations rare k generated by said oscillator', means tending to vary the intensity of said oscillations, means to supply a bias voltage to another grid of said electron discharge oscillator, and means responsive to the amplitude of oscillations rgenerated by said oscillator to control the magnitudeof said bias Voltage thereby to reduce the variations in said amplitude produced rby said first means.

3. The combination, in a superheterodyne signal receiver, a local oscillator, means to combine oscillations produced by said local oscillator with received signals to produce currents of intermediate frequency, means responsive to vartrol the frequency of said local oscillator to main- Atain said intermediate frequency substantially constant, i said last means operating to affect the amplitude of oscillations produced by said local oscillator, and means controlled by said intermediate frequency to oppose the effect of said last means on said amplitude of thezgenerated oscillations.

' 4. In combination, an electron discharge oscillation generator having a plurality of velectrodes and a frequency determining circuit, means responsive to the frequency of oscillations gent means responsive to the frequency of the generated oscillations to affect the amplitude of ,said oscillations in opposite sense to the effect of said frequency regulating means.

verated to control the effective reactance of said 5. The combination, in a superheterodyne signalreceiver, of an electron discharge local oscillator, having a frequency `determining circuit,

`means to combine the oscillations produced by said local oscillator with received signals to pro'- duce currents ofintermediate frequency, means responsive to said intermediate frequency to control the effective reactance of said frequency deduce currents of intermediate frequency, an electron discharge device having an anode and a cathode connected to diierent points on said frequency determining circuit, and having a grid, means to supply oscillations from said frequency determining circuit to said grid in such phase that said discharge device simulates an inductance connected between said points, means to supply a bias voltage to said grid having value dependent upon said intermediate frequency thereby to control said simulated inductance to maintain said intermediate Vfrequency constant, and means to control theamplitude `of said oscillations, said last means comprising an additional grid in said electron discharge oscillator, and `means to control the bias on said additional grid in accordance with said first mentioned bias.

7. The combination in asuperheterodyne receiver, of'an electron discharge device having an anode, a cathode, a control grid and a suppressor grid interposed `between said control grid and anode, a frequency determining circuit connected With said anode and control grid thereby to generate oscillations, means to combine said oscillations with received signals to produce currents having an intermediate frequency, a second electron discharge device having a pair of electrodes connected across said frequency determining circuit thereby to control the frequency determined by said circuit, and having a control grid, means to produce a unidirectional potential dependent in magnitude upon said intermediate frequency, and to supply said unidirectional potential to said suppressor gridand to said last mentioned control grid Whereby the potential on both of said grids is varied with variations in said intermediate frequency.

NORTON F. SHOFSTALL. 

